1. Field of the Invention
The present invention relates to recombinant vectors and cell lines, and methods for detecting and monitoring viral infection. More particularly, the invention relates to recombinant vectors and cell lines, and methods for detecting HIV infection, monitoring HIV for drug resistance and screening for anti-HIV agents.
2. Description of Related Art
Human immunodeficiency virus (HIV) has been implicated as the primary cause of the slowly degenerate disease of the immune system termed acquired immune deficiency syndrome (AIDS). Infection of the CD4+ subclass of T-lymphocytes with the HIV type-1 virus (HIV-1) leads to depletion of this essential lymphocyte subclass which inevitably leads to opportunistic infections, neurological disease, neoplastic growth and eventual death.
Infection with human immunodeficiency virus (HIV) is a chronic process with persistent, high rates of viral replication. The pathogenesis of HIV-1 infection is characterized by a variable but often prolonged asymptomic period following the acute viremic phase. Previous work has established a correlation between HIV disease progression and increasing amounts of infectious virus, viral antigens, and virus-specific nucleic acids (Ho et al., New England. J. Med. 321: 1621-1625 (1989); Schnittman et al. AIDS Res. Hum. Retroviruses 7: 361-367 (1991); Pantalco et al. Nature 362: 355-358 (1993)).
A variety of reagents and assays have been developed to detect the infection of HIV and monitor the progression of HIV in the body. For example, counting the depletion of CD4+ cells has been used to indicate the prognosis of AIDS. Serological screening techniques are also being utilized worldwide for the detection of HIV, where the presence of the antibody against HIV antigens, such as the HIV p24 antigen, is detected.
An ELISA assay is currently being utilized on serum samples in most hospitals and screening laboratories to make the determination. However, currently used ELISA assays may not be sensitive enough to detect all HIV infected individuals. This is because that some HIV infected individuals do not have detectable levels of serum antibody to HIV. There may be a significant time lag between detection of HIV infection and seroconversion. In addition, some HIV infected but seronegative individuals might never convert but will remain infected throughout theirs lives. Thus, such a screening method may generate false negatives, which in turn may increases the probability of HIV infection of healthy people by these individuals.
Another method for detecting HIV infection in seronegative individuals was described (Jehuda-Cohen, T. et al. Proc. Natl. Acad. Sci. UAS, 87: 3972-3076 (1990)) wherein peripheral blood mononuclear cells (PBMC) are isolated from the blood and then exposed to a mitogen such as pokeweed mitogen. Incubation of isolated PBMC with pokeweed mitogen caused the PBMC to secret immunoglobulins that were specific for HIV. The failure of the ELISA assay to detect all HIV infected individuals places the population at risk by misleading the HIV infected individuals that they are not infected, thereby making it more likely that the HIV infected individuals will unknowingly infect others.
The existence of HIV has also been determined by using the reverse transcriptase-polymerase chain reaction (RT-PCR) to amplify plasma HIV RNAs (U.S. Pat. No. 5,674,680). This method is used to detect three types of HIV mRNA in peripheral blood cells: unspliced, multiple spliced, and single-spliced mRNA in AIDs patients, HIV-infected but asymptomatic individuals and individuals who are undergoing therapy for AIDS. However, the correlation between the differences in HIV mRNA levels and AIDS prognosis needs to be established.
Many antiviral drugs have been developed to inhibit HIV infection and replication by targeting HIV reverse transcriptase and proteases. Treatment following a prolonged single drug regimen has met with limited success where there is relatively small drop in viral load, followed by a rise in amount of detectable virus in blood, presumably due to the development of drug resistance strains of HIV. The resistance of HIV to drugs is not only associated with the high mutation rates of HIV but also due to the selective pressure of prolonged anti-HIV drug therapy. Since the original description of diminished susceptibility of isolates of HIV-1 to zidovudine (AZT) (Larder et al. Science (1989) 243:1731-1734), the literature has disclosed many descriptions of diminished susceptibility to AZT in different clinical situations, with different assay systems, and of genetic mutations responsible for changes in susceptibility. For example, isolates from subjects not treated with AZT display a narrow range of susceptibilities to AZT, with the 50% inhibitory concentrations (IC50) ranging from 0.001 to 0.04 μM (Larder et al. (1989), supra; Rooke et al. AIDS (1989) 3:411-415; Land et al. J Infect Dis (1990) 161:326-329; Richman et al. J. AIDS (1990) 3:743-746; Tudor-Williams et al. Lancet (1992) 339:15-19). This narrow range of susceptibilities is typical for HIV isolates from subjects of all ages and at all stages of HIV infection. Isolates of HIV from patients who receive AZT, however, chronically display progressive reductions of susceptibility to AZT over periods of months to years. Diminished susceptibility to AZT of an isolate of HIV-2 from a patient on prolonged therapy has also been reported (Pepin et al. Eighth International Conference on AIDS, Amsterdam, The Netherlands, Jul. 19-24, 1992 Abstract PoA 24401).
In addition to AZT, HIV resistance have been seen with other nucleosides and to nonnucleoside anti-retroviral drugs. For example, isolates resistant to AZT display diminished susceptibility to other nucleosides containing a 3′-azido moiety, including 3′-azido-2′,3′-dideoxyuridine, 3′-azido-2′, ′dideoxyguanosine, and 3′-azido-2′,3′-dideoxyadenosine (Larder et al. (1989), supra; Larder et al. Antimicrob Agents Chemother (1990) 34:436-441). Additionally, AZT-resistant isolates are reported to display cross-resistance to didehydrodideoxythymidine (Rooke et al. Antimicrob. Agents Chemother. (1991) 35:988-991).
Drug resistance in HIV isolates is not limited to inhibitors of reverse transcriptase and virtually all drug targets for anti-HIV therapy are susceptible to the development of resistance. For example, a mutant with resistance to a protease inhibitor has been isolated that exhibits an eightfold reduction in susceptibility to a protease inhibitor (Patterson et al. Eighth International Conference on AIDS, Amsterdam, The Netherlands, Jul. 19-24, 1992, Abstract ThA 1506).
In the last five year, with the fast development of anti-HIV drugs and utilization of combination therapy, treatment of HIV infection with multiple antiviral drugs (“cocktails”) have led to diminutions in the amount of viral RNA and virus detectable in blood by using current detection methods. It has been shown that combination therapy with 3 or more antiviral drugs, e.g. indinavir, zidovudine, and lamivudine, or alternatively, nevirapine, zidovudine, and didanosine, in previously untreated patients has resulted in profound decreases in viral burden (Wainberg, M. A. and Friedland, G. JAMA (1998) 279: 1977-1983). It was believed that the combination antiviral regimens used must have blocked viral replication to the extent that the mutations that encode drug resistance could not occur. However, current studies showed that a growing number of patients are failing combination drug regimens (Deek, S. et al. the 5th Conference on Retroviruses and Opportunistic Infection, Chicago, Feb. 1-5, 1998, Abstract #419). Finding an effective salvage therapy for them is difficult.
In the clinical setting, drug resistance is often not detected until a patient manifests symptoms of disease progression, which is generally not observed until significantly after development of a drug resistant strain of virus. Thus, there is a clear need for an assay which can indicate the drug resistance of virus strains so drug therapy for a patient can be modified accordingly, and optimally as soon as resistance is detected rather than delaying until clinical symptoms are observed.
Currently the most commonly used assays for susceptibility of HIV to antiviral drugs involve the measurement of the inhibition of cytopathology, p24 production, or reverse transcriptase production of a laboratory strain of HIV in a lymphoblastoid cell line. Such assays may not be readily applied to clinical isolates of HIV. Examples of commonly used assays of drug susceptibility of clinical isolates have been the syncytial focus assay in CD4-HeLa cells (Chesebro, B. and Wehrly, K., J. Virol. (1988) 62:3779-3788), inhibition of p24 production in primary peripheral blood mononuclear cells, and reverse transcriptase (RT) assays using cultured primary T-cells from patient blood. (Richman et al. In: Current Protocols in Immunology, Coligan et al., eds, (1993) Brooklyn, J. Wiley).
One of the disadvantages associated with the syncytial focus assay is that it may only detect HIVs that exhibit a syncytial-inducing phenotype and that in practice may only be obtained from a minority of specimens from seropositive individuals. And the syncytial focus assays may not be used for screening for drugs that affect posttranslational processing, such as glycosidase and protease inhibitors. On the other hand, the p24 and RT assays may also suffer the limitations of difficult quantification, low sensitivity and unproven clinical validity.